[GHC] #10965: GHC Panic on import with 'OPTIONS_GHC -fobject-code -O'

[GHC]

#10965: GHC Panic on import with 'OPTIONS_GHC -fobject-code -O'
---------------------------------+--------------------------------------
        Reporter:  Orome         |                Owner:
            Type:  bug           |               Status:  new
        Priority:  normal        |            Milestone:
       Component:  Compiler      |              Version:  8.0.1-rc2
      Resolution:                |             Keywords:
Operating System:  MacOS X       |         Architecture:  x86_64 (amd64)
 Type of failure:  None/Unknown  |            Test Case:
      Blocked By:                |             Blocking:
 Related Tickets:  #10549        |  Differential Rev(s):
       Wiki Page:                |
---------------------------------+--------------------------------------

Comment (by rwbarton):

 The contents of the module aren't relevant, this module exhibits the same
 panic.
 {{{
 {-# OPTIONS_GHC -fobject-code -O #-}

 f :: String -> String
 f = id
 }}}

 The difference is that this module has `-fobject-code`. `checkOptLevel`
 disallows `-O`, if the target is `HscInterpreted`. That was the fix for
 #10549. But here the target is `HscAsm`.

 But somewhere later the target must get set to `HscInterpreted`, as
 evidenced by the output
 {{{
 [1 of 1] Compiling Main             ( G.hs, interpreted )
 }}}
 and the fact that the module contains breakpoints. (So as another issue,
 `{-# OPTIONS_GHC -fobject-code #-}` doesn't actually work. Seems it hasn't
 worked since at least 7.8.)

 Aha, found it!
 {{{
 upsweep_mod hsc_env old_hpt (stable_obj, stable_bco) summary mod_index
 nmods
    =   ...
             -- We're using the dflags for this module now, obtained by
             -- applying any options in its LANGUAGE & OPTIONS_GHC pragmas.
             dflags = ms_hspp_opts summary
             prevailing_target = hscTarget (hsc_dflags hsc_env)
             local_target      = hscTarget dflags

             -- If OPTIONS_GHC contains -fasm or -fllvm, be careful that
             -- we don't do anything dodgy: these should only work to
 change
             -- from -fllvm to -fasm and vice-versa, otherwise we could
             -- end up trying to link object code to byte code.
             target = if prevailing_target /= local_target
                         && (not (isObjectTarget prevailing_target)
                             || not (isObjectTarget local_target))
                         then prevailing_target
                         else local_target

             -- store the corrected hscTarget into the summary
             summary' = summary{ ms_hspp_opts = dflags { hscTarget = target
 } }
        ...
 }}}

 Assuming this stuff about linking object code and byte code is still
 relevant, I guess we should call `checkNewDynFlags` on `dflags { hscTarget
 = target }`.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10965#comment:4>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler